The present invention generally relates to a mobile communications technique, and more particularly to a mobile communications system that manages mobility of a mobile terminal in a network and to a routing manager used in the mobile communications system.
Various studies have been made on Internet Protocol (IP) based mobile communication networks.
FIG. 1 is an example of such an IP based mobile communications system. The system 100 includes a first network 102 managed by a telecommunication carrier to provide mobile telephone services, a second network 104 managed by the same or a different telecommunication carrier to provide mobile telephone services, and a third network 106, such as the Internet, connecting the first and second networks 102 and 104. Signal transmission of a mobile terminal in the first network 102 is managed by a first local routing manager (LRMs) 108. The lower case letter “s” denotes a sender, which in this case is the mobile terminal 120. The lower case letter “r” described below denotes a receiver, which in this example is a counterpart destination mobile terminal 136. It is needless to say that the mobile terminal 120 and the counterpart destination terminal 136 function as both senders and receivers during telecommunications.
In the first network 102, an anchor router (ANRs) 110 and access routers (ARs) 112 and 114 connected under the anchor router 110 are arranged. The access routers 112 and 114 have cells 116 and 118, respectively, which are prescribed geographic areas controlled by these access routers. The access routers 112 and 114 are capable of communicating with mobile terminals located in the associated cells. In the example shown in FIG. 1, the mobile terminal 120 is located in the cell 116 of the access router 112. ANRs 110 delivers or routes a received packet to access router 112 or 114 according to the routing management scheme of LRMs 108. The LRMs 108 manages a table of received packets (TRP) that describes how the address of the packet received at the ANRs 110 is to be converted for routing the packet. In general, there is one or more anchor routers in a network. When using multiple anchor routers, the network is divided into multiple sections, and packet routing efficiency is improved.
Similarly, signal transmission of a mobile terminal in the second network 104 is managed by a second local routing manager (LRMr) 122. In the second network 104, access router (oARr) 128 connected under anchor router (oANRr) 124, and access router (nARr) 130 connected under anchor router (nANRr) 126 are arranged. The lower case letters “o” and “n” denote old and new, respectively, which represent before and after handover between cells. The access routers 128 and 130 have cells 132 and 134, respectively, which are prescribed geographic areas controlled by these access routers. The access routers 128 and 130 are capable of communicating with mobile terminals located in the associated cells. In the example shown in FIG. 1, the counterpart terminal 136, which is in communication with the mobile terminal 120, is located in the cell 132 of the access router 128. Anchor routers 124 and 126 deliver or route a received packet to the associated access routers 128 and 130, according to the routing management scheme of LRMr 122. The LRMr 122 manages a table of received packets (TRP) that describes how the address of the packet received at each of the anchor routers is to be converted for routing the packet.
The mobile communications system 100 also includes home routing manager (HRMr) 138. Home routing manager (HRMr) 138 manages the correspondence between the unique IP home address “IPhar” of the counterpart terminal 136 and the address “ANRr.x” used in the network in which the counterpart terminal 136 is currently located as a visitor. Home address “IPha” is an unchanging IP address assigned to each terminal, regardless of which network the terminal is currently visiting. In the network, an IP routing address “IPra”, such as “AR.x”, is also used. This IP routing address is a temporary address assigned by the associated access router to the terminal located in the cell. The mobile communications system 100 further includes home routing manager (HRMs) 140, which manages the correspondence between the unique IP home address “IPhas” of the mobile terminal 120 and the local address “ANRs.x” used in the network in which the mobile terminal 120 currently exists.
FIG. 2 is sequence diagram showing a sequence carried out when telecommunication is started between the mobile terminal 120 and the counterpart destination terminal 136 in the mobile communications system 100 shown in FIG. 1. First, as indicated by step 202, the mobile terminal 120 transmits a data packet addressed to the counterpart terminal 136, designated by the home address “IPhar”, to the access router 112 to which the mobile terminal currently belongs. The access router 112 refers to the table of sending packets (TSP) to determine to which access router or anchor router the packet with address “IPhar” is to be transferred. If the table of sending packets defines the address for accessing the counterpart destination terminal 136, then the access router 112 converts the address held in the data packet to the new address described in the table of sending packets in order to route the packet.
If there is no information about the counterpart destination terminal 136 in the table of sending packets, then the access router 112 queries the home routing manager (HRMr) 138, which manages the IP home address “IPhar” of the counterpart terminal 136, about the information of the counterpart destination terminal 136, as indicated in step 204. Then, in step 206, the access router 112 acquires the address required to access the counterpart terminal 136. Since in the example shown in FIG. 1 the counterpart destination terminal 136 is located in cell 132 controlled by access router 128 under the anchor router 124, the home routing manager HRMr 138 manages the home address “IPhar” in association with address “oANRr.x” given under the anchor router 124. The latter address is reported to the access router 112. Upon receiving the current local address, the access router 112 creates a new entry in the table of sending packets so as to convert the home address “IPhar” of the counterpart terminal 136 into address “oANRr.x” assigned under anchor router 124.
In FIG. 2, double arrows (such as step 202) represent a signal transmission containing a data packet transmitted between the mobile terminal 120 and the counterpart terminal 136. The single arrows (such as step 204) represent transmission of control signals that do not contain substantial data packets.
Hereinafter, address “IPhar” of the data packet having arrived at the access router 112 is converted to address “oANRr.x”, and the address-converted packet is transmitted in the network, as in step 208.
Then, in step 210, the anchor router 124 converts the address “oANRr.x” of the received packet to “oARr.x”, based on the table of received packets (TRP), and transmits the address-converted packet to the access router 128 arranged under this anchor router 124. The contents of the table of received packets (that is, converting “oANRr.x” to “oARr.x”) are defined by LRMr 122 that manages the locations and the mobility of the cellular terminals existing in the network 104. The access router 128 gives the address “oARr.x” to the counterpart terminal 136 for telecommunications when the counterpart terminal 136 has entered the cell 132, and records the correspondence between the local address and the home address of the counterpart terminal 136 (indicating address conversion from “oARr.x” to “IPhar”) in the table of received packets (TRP).
Accordingly, upon receiving the data packet addressed to “oARr.x”, the access router 128 converts this address to “IPhar” according to the table TRP, and transmits the address-converted packet to the counterpart destination terminal 136, as in step 212. In this manner, the data packet transmitted from the mobile terminal 120 is correctly delivered to the counterpart destination terminal 136.
Next, when the counterpart terminal 136 responds to the mobile terminal 120, the access router 128 receives a data packet addressed to the home address “IPhas” of the mobile terminal 120 in step 214. The subsequent procedures are the same as those in steps 202 through 212. The access router 128 checks the table of sending packets in order to convert the home address “IPhas” of the mobile terminal 120 to the appropriate address. If there is information about the address conversion defined in the transmission table TSP, the home address of the data packet is converted to the local address indicated by the transmission table TSP for further transmission.
If there is no information about address conversion of the mobile terminal 120 in the transmission table TSP, then the access router 128 requests information about the mobile terminal 120 from the home routing manager (HRMs) 140, which manages the IP home address “IPhas” of the mobile terminal 120, as indicated in step 216. Then, the access router 128 acquires address “ANRs.x”, which is given under the anchor router 110 and managed in association with home address “IPhas”. The access router 128 creates a new entry in the table of sending packets TSP so as to convert the home address “IPhas” of the mobile terminal 120 into address “ANRs.x” assigned under anchor router 110.
Hereinafter, address “IPhas” of the data packet having arrived at the access router 128 is converted to address “ANRs.x”, and the address-converted packet is transmitted in the network, as in step 220.
Then, in step 222, the anchor router 110 converts the address “ANRs.x” of the received packet to “oARs.x”, based on the table of received packets (TRP), and transmits the address-converted packet to the access router 112 arranged under this anchor router 110. The contents of the table of received packets (that is, converting “ANRs.x” to “oARs.x”) are defined by LRMs 108 that manages the locations and the mobility of the cellular terminals existing in the network 102. The access router 112 gives the address “oARs.x” to the mobile terminal 120 when the mobile terminal 120 has entered the cell 116 for telecommunication, and records the correspondence between the local address and the home address of the mobile terminal 120 (indicating address conversion from “oARs.x” to “IPhas”) in the table of received packets (TRP).
Accordingly, upon receiving the data packet addressed to “oARs.x”, the access router 112 converts this address to “IPhas” according to the table TRP, and transmits the address-converted packet to the mobile terminal 120 located in the cell 116, as in step 224. In this manner, the data packet transmitted from the counterpart terminal 136 is correctly delivered to the mobile terminal 120.
Since when a data packet is relayed at each node, address conversion is conducted, rather than encapsulation, overhead can be prevented from increasing. Accordingly, packet transmission can be performed efficiently. In addition, in telecommunication between the mobile terminal and the counterpart terminal, only each other's home addresses are used, and the routing address (for example, “ARr.x”, “oARs.x”, etc.) containing the location information of the cellular terminal is concealed in the network. Consequently, privacy of the user is protected. Concerning the above-described type of mobile communications system, see “Mobility Management Architecture for IP-based IMT Network Platform”, M. Sawada, et al., IEICE Society Conference, September 2002.
FIG. 3 shows the communications sequence during handover of the mobile terminal 120 between cells, which could happen after the sequence shown in FIG. 2. In this example, the mobile terminal 120 currently located in cell 116 and in communication with the counterpart terminal 136, is moving to another cell.
To allow the handover of the mobile terminal 120, the tables of received packets stored in the anchor router 110 and a new access router 114 have to be updated so as to forward incoming packets addressed to the mobile terminal 120 to the new access router 114. The table of received packets of the access router 114 may be updated when the access router 114 assigns address “nARs.x” to the mobile terminal 120. The table of received packets of the anchor router 110 is updated based on the notification transmitted from the new access router 114 to the LRMs 108 in step 301. The LRMs 108 instructs anchor router 110 to update the table of received packets in step 303.
In addition to updating the table of received packets, the access router 114 has to create a new entry in the table of sending packets TSP. As indicated in step 305, when receiving data packets addressed to home address “IPhar” of the counterpart terminal 136 from the mobile terminal 120, the access router 114 searches in the table of sending packets. However, it is currently unknown to which address the home address “IPhar” of the counterpart terminal 136 be converted because there is no past record of sending packets from this access router 114 to the counterpart terminal 136.
Accordingly, in step 304, the access router requests the information about the counterpart terminal 136 from the home routing manager HRMr 138 that manages the home address “IPhar” of the counterpart terminal 136, if the table of sending packets does not have the information. Then, the access router 114 acquires information about the local address currently used by the counterpart terminal 136 in step 306. Based on the information, the access router 114 creates a new entry representing address conversion of the home address “IPhar” of the counterpart terminal 136 into “oANRr.x” assigned under the anchor router 124.
When the new entry is recorded in the table of sending packets, the data packets addressed to the counterpart terminal 136, which have been buffered in the access router 114, are transmitted to the anchor router 124, as in step 308. Then, the data packets are forwarded to the counterpart terminal 136 in steps 310 and 312.
However, this method has a problem because HRMe 138 is generally far away from network 102, and therefore, the requesting and responding (steps 304 and 306) between the access router 114 and HRMr 138 are likely to take a long time. This results in undesirable delay in creating a new entry in the table of sending packets at the new access router. Unless the new entry is recorded in the table of sending packets, the data packets buffered in the access router cannot be transmitted. This makes it difficult to carry out handover, while transmitting data packets continuously. Especially, since the requesting sequence from the access router 114 (such as steps 304 and 306) is started after the receipt of data packets transmitted from the mobile terminal 120 to the counterpart terminal 136, the data packets are buffered in the access router 114 until the requesting sequence is completed and the table of sending packets is updated. It is a concern that the buffering delay becomes undesirably long. In addition, as the time required to update the table of sending packets becomes greater, the volume of data packets buffered in the access router 114 becomes large, and therefore, a large-capacity memory is required.
FIG. 4 shows a communications sequence during handover of the counterpart terminal 136 between cells, which could also happen after the sequence shown in FIG. 2. In this example, the counterpart terminal 136 is moving from cell 132 to another cell 134. If the handover is conducted between access routers under the same anchor router 124, the tables of received packets of the new access router 130 and the anchor router 124 can be updated using the same procedure as shown in steps 301 through 306. In this case, the same problem as has been described in connection with FIG. 3 occurs.
The handover sequence illustrated in FIG. 4 is one conducted between access routers under different anchor routers. In step 402, the counterpart terminal 136 accesses the new access router 130. The access router 130 creates a new entry in the table of received packets so as to associate the local address “nARr.x” assigned by the access router 130 with home address “IPhar” of the counterpart terminal 136.
Then, in step 404, the access router 130 requests LRMr 122 to update the table of received packets stored in the new anchor router 126. In response to the request, LRMr 122 and the new anchor router 126 update the tables of received packets so that address “nANRr.x” is associated with address “nARr.x” assigned by the access router 130, as in step 406.
Then, in step 408, LRMr 122 requests HRMr 138 to update the record so as to associate the home address “IPhar” of the counterpart terminal 136 with address “nANRr.x” assigned under the new anchor router 126.
Then, in step 410, the HRMr 138 reports the updated correspondence between the home address “IPhar” of the counterpart terminal 136 and the new local address “nANRr.x” assigned under the anchor router 126 to the access routers and other nodes that have queried HRMr 138 about the counterpart terminal 136 in the past. In this particular example, the access router 112 has queried HRMr 138 in steps 204 and 206 in FIG. 2, and HRMr 138 stores this record. Upon receiving the report from HRMr 138, the access router 112 updates the table of sending packets so as to convert the home address “IPhar” of the counterpart terminal 136 into “nANRr.x”. In the subsequent process, the packets addressed to the counterpart terminal 136 are correctly delivered to the counterpart terminal 136 located in the new cell.
However, because the table of sending packets of the access router (step 410) is updated via HRMr 138, which in general is located far away from the first and second networks 102 and 104, time required to update the table of sending packets may be undesirably increased. Unless the table of sending packets of the access router 112 is promptly updated, a number of data packets may be transmitted to the previous anchor router 124 having functioned before the handover, depending on case. This may result in decreased transmission efficiency.